1. Field of the Invention
The invention relates to microwave hybrid junctions as switches.
2. Description of the Prior Art
Microwave hybrid junctions are four terminal devices which ideally have the property that power supplied to a given terminal is divided usually equally between two of the remaining terminals with nothing reflected back or coupled to the fourth terminal. However, by appropriate positioning of short circuits in said two of the remaining terminals (control terminals), the energy provided to them can reflect to return to the input or add at the fourth terminal. A selectively forward or reverse biased diode can effect electrical movement of a short circuit location so as to switch the path from the given terminal to the fourth terminal between open and closed conditions. A particular advantage of this type of arrangement is that the power from the given terminal splits between the two control terminals whereby a diode located in one of them never sees more than half the power.
In U.S. Pat. No. 3,559,108 to H. Seidel, coupler switches are disclosed using both the quadrature and 180.degree. type of hybrid junctions. Seidel uses pairs of variable impedances such as a diode for each of the control terminals. Also for modulation, demodulation, phase inversion or switching, the symmetrical arms of a T-junction are conventionally used for control. The nonsymmetrical arms become the signal in and out ports. This is the kind of configuration Seidel uses as is clear from his statement (column 6, lines 72-73), the 180.degree. coupler switch is open in its symmetric state. When using the nonsymmetrical arms for control, as in the present invention, symmetrical impedances in the control arms close the switch. The asymmetry of the nonsymmetrical arms has made it virtually impossible to design control elements in those arms from a strictly theoretical approach. As a result the symmetrical arms have always provided the control function. Using the nonsymmetrical arms for input/output functions raises problems of packaging, particularly in waveguide.
For the most compact insertion of a switch in many waveguide systems, the input/output ports are preferably colinear. The symmetrical arms of a hybrid T-junction are readily colinear while the nonsymmetrical arms are not.
U.S. Pat. No. 3,93l,599 to the present inventor discloses a phase invertor using asymmetrical switching in the main arms to produce phase inversion. As with Seidel, variable impedances are provided at both control terminals.